howdy, my first post! thanks for the informative posts, after I suspected bump steer problems I looked around here and seems the problem happens now and then. usually an air bag or strut problem.

I just bought a certified car and have already put 3k miles on it. I love the car, my first Mercedes. It has a really bad bump steer problem though. At slow speeds and high speeds the rear end jumps out, especially bad of course when already steering input.

I bought it from out of state, but just took it in for the first time to Park Place Grapevine Mercedes. They checked the suspension and alignment, they didn't find anything. I am disappointed, but doesn't surprise me a tech wouldn't be sensitive to the problem not hitting the right bumps, right angle, right speed, whatever.

The only possible explanation that there is nothing wrong would be the car has some driving aides etc that over bumps make it feel like a more analog car with bump steer. I doubt this is the case because even the passengers notice something is wrong as the rear end hops out.

I have reached out to one of my friends who use to race for Park Place professionally to see if he can confirm what I'm feeling and to see if he still has any contacts.

Otherwise I feel a little helpless. They have looked at the suspension, checked the alignment, and test drove it not indicating anything wrong. I swear I'm right, but not sure how to prove it to the dealer. Of course when I said let me take you for a test drive, they balked because of Covid. I then asked to test drive a similar model and surprisingly the service advisor didn't seem too positive about that either.

Beyond that all good. FYI I got the 1 year CPO warranty +2 and I have a faulty drink cooler/heater, which isn't covered by the warranty and $1,400.

 

Welcome! Nice looking AMG. Please describe the precise conditions where you experience the situation. Others can make helpful suggestions with a complete picture of what you are experiencing.

 

• highway speeds like bridge span joints the rear end feels like stepping out. any more abrupt bump does this as well.
• slow speeds (25-40 mph) does it as well, there is a spot by my house where concrete had spilled at one time and that's enough to do it.
• always more severe in a turn already some steering input.
• even without bumps there seems to be an odd "rock the boat" float to the suspension.

It is very disconcerting and I told the service advisor not safe and he brushed it off. Understand the good and bad on one hand I'm pretty forgiving of cars as I've had several high performance cars and I know what makes them handle great on the track is usually opposite of what feels good on the street. On the flip side I raced for many years so a little bit extra sensitive to the handling of the car. I expected and I want this car to be just tolerable on the streets and I don't want it to understeer being that comfy, but to me unacceptable to have the rear end step out this much.

 

I would call what you are describing as axle hop rather than bump steer. Bump steer has a specific definition which means the change in toe (steer) angle of a tire as it travels through jounce (upward) and rebound (downward) suspension movement. Your description is when the rear of the vehicle steps out when the rear suspension travels over a discrete bump or imperfection. Do you agree?

How many miles are on the vehicle?

What size wheels and tires do you have? Look very carefully at the tires, particularly on the rear axle. Please describe what you see, or better yet, post clear closeup photos of the tires.

 

Does it feel unstable in Sport mode? I had one that had a shock go bad and when you put it in sport mode it was much less noticeable. Replaced both rear shocks and air bags at the same time. Felt like new again.

 

What is your tire pressure? I would try to lower it by 5 PSI and see if the behavior improves.

 

I might agree, to me it gets really unstable, but it might not be the steering changing, you are right it might be the axle side stepping.

56k now.

22", whatever the stock MB tires are. I'll get the car back today and take pics. I did have them do a rotation. thanks!

 

I played with this, but happens in all modes.

 

I checked pressures before our trip and it was to manufacturer recommendation, something like 45-48. I don't think the abrupt nature of this could be related to 5 pounds +/-.

 

I venture to say it’s normal, the behavior you are experiencing. This is based on my experience with 20” wheels on a GLE. 22” wheels on an AMG GLS will be as bad, or worse. Modern wheel+tire+suspension combination is poor for sporty vehicles, as far as comfort is concerned. I’m putting the side stepping behavior in the category of absence of comfort.

 

Hi I am having the same thing now, where any bump or any road that is not literally perfect will make the car unstable. Were you able to find a fix